Miniature multiple-diaphragm acoustic mechanoelectric transducer device

ABSTRACT

A miniature size electroacoustic signal transducer device has an elongated mechanoelectric transducer connected to a plurality of diaphragms for multiplying the transduced signal output.

United States Patent William F. Knauert Yonkers, N.Y.

Jan. 26, 1970 May 18, 1971 Sonotone Corporation Elmsford, N.Y.

Inventor Appl. No. Filed Patented Assignee MINIATURE MULTl PLE-DIAPHRAGM ACOUSTIC MECHANOELECTRIC TRANSDUCER DEVICE 5 Claims, 10 Drawing Figs.

U.S. Cl l79/ 139, 179/ 1 10 int. Cl H04! 7/00 [50} FieldofSearch 179/110.1, 110.4. 132. 139

{ 56] References Cited UNITED STATES PATENTS 2,773,942 12/1956 Christensen 179/1 10(. 1) 3,181,016 4/1965 Rosenman l79/11OX(.1)

Primary E.taminer-Ralph D. Blakeslee Attorney-Ostrolenk, Faber, Gerb & Soffen ABSTRACT: A miniature size electroacoustic signal transducer device has an elongated mechanoelectric transducer connected to a plurality of diaphragms for multiplying the transduced signal output.

mente'd May 18, 1971 3,578,921

2 Sheets-Sheet 2 MINIATURE MULTIPLE-DIAPHRAGM ACOUSTIC MECHANOELECTRIC TRANSDUCER DEVICE This application is a continuation of application Ser. No. 634,736, filed Apr. 28, 1967, and now abandoned.

Mechanoelectric acoustic transducer devices which are used in subminiature size hearing aids are usually designed to obtain a maximum signal output of optimum quality. Such transducer devices require maximum subminiaturization. For example, when used as a microphone in a miniature hearing aid worn hidden within an eyeglass temple or behind or within the ear of the user, it is important that it delivers maximum signal output of good quality.

The present invention solves the problem of providing such acoustic signal transducer of subminiature dimensions, e.g., by providing, for example, a hearing aid microphone having external dimensions of 1.100 inch X 0.300 inch X inch and operating with known-type elongated electromechanical piezoelectric or piezoresistive transducers. The elongated transducer may be either of the piezoelectric or piezoresistive type such as described, for instance, in U.S. Pat. Nos. 2,863,076 (Koren et al. or 3,089,108 (Gong et al.)

In a subminiature acoustic transducer device of the invention an elongated vibratory mechanoelectric transducer of miniature dimensions is vibratably mounted within a cavity of a correspondingly shaped miniature housing having at least one housing wall overlying at least one side of the elongated transducer surfaces. Along different housing wall sections are vibratably mounted at least two different acoustically excitable diaphragms, each connected by a drive rod to a different longitudinally displaced section of the elongated transducer. The housing has a plurality of longitudinally displaced curved bearing surfaces which engage longitudinally displaced bearing-contact surfaces on opposite surfaces of the elongated transducer for maintaining it in an efficient operative vibratory signal transducing position or condition.

As one example, such electroacoustic transducer device of the invention has at least two such diaphragms vibratably mounted or carried along laterally displaced portions of one housing wall and connected by different distinct driving rods to different longitudinally displaced connector sections of the transducer. At least one portion of the elongated transducer disposed between two of its diaphragm-connector rods has at least one set of its opposite transducer surface portions engaged by a set of curved bearing surfaces of or carried by the housing. The curved bearing surfaces maybe formed by facing portions of the housing or by curved bearing surfaces of metal rods suitably mounted within the housing. Such metallic bear-' ing rods also serve as circuit connections to opposite polarity electrode surfaces exposed on the opposite surfaces of the elongated transducer.

In one example of the invention, two vibratory acoustic diaphragms are operatively supported along laterally displaced sections of one housing wall. Two longitudinally displaced transducer portions have drive-rod connections to the two diaphragms. At least one set of opposite surface portions of an intermediate portion of the transducer length is engaged by an associated one set of opposite curved bearing surfaces of the housing and constituting its operative vibratory bearing support for causing the elongated transducer to supply a signal output corresponding to the acoustic input to the two diaphragms and vice versa. In another example of such twodiaphragm electroacoustic transducer device, two longitudinally displaced sets of curved housing bearing surfaces engage two correspondingly displaced sets of opposite bearing contacted surfaces of the elongated transducer, with these two sets of displaced bearing surfaces being disposed between the two driving connections of the elongated transducer to the two acoustic diaphragms.

As a' further example, such multiple-diaphragm electroacoustic transducer device has a third acoustic diaphragm along a housing wall extending opposite the housing wall carrying the two laterally displaced acoustic diaphragms. Such third diaphragm has a similar drive rod connection to a portion of the elongated transducer disposed between its associated two sets of opposite bearing surfaces of the justdescribed other example.

At least two of the curved housing bearing surfaces are fonned by mutually insulated metallic rods which engage opposite metallic electrode surfaces exposed along the opposite exterior surfaces of the elongated transducer for providing electric circuit connections to the electromechanical transducer structure thereof.

It is a primary object of the present invention to maximize the signal output of a miniature size mechanoelectric acoustic transducer device.

It is a further object of the present invention to maximize the signal output of a miniature size mechanoelectric transducer device having a plurality of diaphragms which are connected with a single transducing member in aiding signaltransducing relation.

These and other objects of the present invention will become apparent from the following description of examples thereof in conjunction with the accompanying drawings wherein:.

FIG. 1 is a vertical cross section through a transducer device exemplifying the invention;

FIG. 1A shows how a transducer device of the instant invention may be worn by the user;

FIG. 2 is a cross section of the device along the line 2-2 of FIG. 1;

FIG. 3 is a cross section similar to FIG. 1 of the transducer housing;

FIG. 4 is a plan view of the housing along line 4-4 of FIG. 3; FIG. 5 is a plan view of the diaphragm alongline 5-5 of FIG.

FIGS. 6 and 7 illustrate two types of piezoelectric transducer elements suitable for transducer devices of the inventron;

FIGS. 8 and 9 are circuit diagrams of two systems operating with piezoelectric elements shown, respectively, in FIGS. 6 and 7.

FIG. 1A illustrates one of the many uses for the transducer device of the invention. Such transducer device of the invention makes possible its miniaturization and incorporation in a hearing aid small enough for hidden wear within the rear portion 10 of the temple ll of eyeglass frames 12 or behind or within the ear of the user. To simplify the disclosure, the examples of the invention will be described herein as operating with known elongated strip-shaped piezoelectric ceramic transducers 40 or 50 shown in FIGS. 6 and 7 although other types, such as similarly shaped piezoresistive transducers, may be used instead.

FIGS. 1 to 4 show one example of an electroacoustic transducer device of the instant invention. Although the FIGS. show a three-diaphragm electroacoustic device of the invention, such device operating with two diaphragms along one housing wall will supply a signal output approaching that obtainable with three diaphragms. It comprises a single housing structure 20 having one sidewall 25 operating with at least two laterally displaced acoustic diaphragms 70. The housing 20 may be made of an insulating material such as polystyrene plastic. If, however, the housing is to serve as an electric conductor connection for the transducer member or element, the housing or part thereof might be made of a conductive material. One sidewall of the housing wall 25 has a plurality of diaphragm receiving apertures 21 and 22 which open into the acoustic cavity 24 of the housing (FIGS. 1, 2, 3, 4). The principal distinction of the present invention resides in a subminiature acoustic transducer device such as a hearing aid microphone, for example, wherein a single elongated electromechanical transducer 40 (or 50) has driving coupling connections with two vibratory acoustic diaphragms 70 mounted on wall surface 28 and laterally displaced along one overlying sidewall of the housing 20. However, in some applications, such acoustic transducer of the invention may be provided with a third diaphragm. For conciseness sake, the invention will be described in connection with FIGS. 1 to 5 wherein a single elongated transducer 40 operates with three driving connections to three acoustic diaphragms seated along the housing wall surfaces.

It should be understood, however, that the basic feature of the invention comprises a subminiature acoustic device wherein a single elongated electromechanical transducer, such as transducers 40 or 50 of FIGS. 6 or 7, for example, have driving connections to two vibratory acoustic diaphragms carried in laterally displaced positions along one sidewall of the housing overlying such elongated transducer 40 or 50.

Thus, in the example of FIGS. 1 to 5, two main laterally displaced diaphragm apertures 21 and 22 extend along a first or upper housing wall 25 and a third diaphragm aperture 23 along an opposite'housing wall 26. Such diaphragm-transducer combination enables the several hereinbelow described diaphragms 70 to flex the elongated transducing member 40 to the maximum extent, or vice versa.

Each aperture 21, 22, 23 of the housing walls 25, 26 having peripheral shelves 28 along each housing aperture 21, 22 and 23 for seating or carrying the peripheries 71 of the respective acoustic diaphragms 70 in a vibratory condition. The housing walls 25 and 26 have notches 29 for holding therein diaphragm-protective covers or grilles 90. The interior side of the housing wall 25 has a cutout 30 within which a hereinafterdescribed central diaphragm-drive rod 80 may move free of interference.

Within the housing is carried in a vibratory transducer condition or mode a known type of elongated electroacoustic transducer strip or beam 40. The transducer strip may consist of a known piezoelectric or piezoresistive type. For the sake of simplicity, the examples of the invention will be described in connection with known piezoelectric laminated ceramic transducer types having on its opposite surfaces metallic electrode surfaces for impressing an electric signal input to the transducer 40 (or 50) which causes it to vibrate and vice versa. Two examples of different suitable piezoelectric transducers are shown in FIGS. 6 and 7.

Referring to FIG. 6, the elongated thin piezoelectric transducer 40 comprises a sandwich having overlapping planar strips 41 and 42 of known piezoelectric ceramic material. See, for instance, US. Pat. No. 2,708,244. Each ceramic strip 41, 42 has outward and inward electrically conductive metallic electrode coatings 43a, 43b and 43c, 43d, respectively. Sandwiched between the ceramic strips 41 and 42 may be a thin metallic strip 44 which metallically and electrically joins the ceramic strips 41 and 42 at their interface electrode surfaces 43b, 43c into a unitary thin but mechanically strong elongated transducing member or transducer 40.

The interior sides of the housing walls carry curved bearing surfaces which engage the facing surface portion of the opposite exposed outward surfaces of the elongated transducer 40 for maintaining it in an efficient operative signal transducing vibratory condition. The curved surfaces may be formed by inward projections of the opposite housing walls 22, 26. In the example shown, the curved bearing surfaces are formed by two spaced sets or pairs of opposite cylindrically shaped metallic rods 61, 62 and 63, 64 maintaining bearing engagement with the facing opposite outward bearing contact surface portions along two longitudinally spaced regions of the elongated transducer 40 for maintaining it in the desired signal transducing mode as it vibrates in a direction transverse to its major planes or surfaces.

In the piezoelectric ceramic transducer 40 (FIG. 6) its two piezoelectric strips are electrically polarized for operation in aiding relation, for instance by connecting the opposite outward electrode surfaces 430 and 43d between polarizing terminals 45 and 46 as indicated in FIGS. 6 and 8. When such elongated transducer 40 (or transducer 50 of FIG. 7) is flexed or vibrated transversely to its planes or major opposite surfaces, it generates a signal voltage which is supplied to its terminals 45 and 46 and vice versa.

FIG. 7 shows an alternate type of suitable elongated piezoelectric transducer 50 having the same shape as the transducer 40 of FIG. 6. The piezoelectric transducer 50 combines two overlapping piezoelectric ceramic strips 51 and 52 having a set of opposite-polarity metallic surface electrodes 54a, 54b and 54c, 54d, respectively. The inward electrode surfaces 54b and 54d of the two piezoelectric strips are joined to each other by a central metallic strip 53 into the piezoelectric transducer unit 50. The metallically conductive electrode surface coatings of transducer strips 51, 52 are used in a unique and special arrangement. The exterior surface electrode 54a extends over most of the exterior surface of piezoelectric ceramic strip 51. Its opposite-polarity electrode surface coating 54b extends over a small end portion of the exterior surface of piezoelectric ceramic strip 51, curls around its right end at 56 and extends beneath and over the entire interior surface of this piezoelectric ceramic strip 51. The metallic electrode surface coatings 54a, 5412 along the exterior surface of piezoelectric ceramic strip 51 are separated by an insulator, e.g., gap 55, to electrically separate them from each other. This insulating gap 55 is placed near the rightward bent-over upper end portion of electrode coating 56 of transducer strip 51 leaving a maximum length of exterior surface electrode coating 54 on the exterior surface of piezoelectric strip SI, The lower piezoelectric ceramic strip 52 has metallic electrode surface coatings 54c and 54d, respectively, along the entire length of its major upper and lower surfaces.

Referring to FIGS. 7 and 9, the exterior electrode surface coatings 54a and 5411 along the opposite exterior surfaces of transducer 50 of transducer strips 51, 52 are electrically connected to each other by bridging conductor 58 and have the same electric potential. This may be done by the conductor 58 connecting the metallic bearing rods 61, 62 which maintain electric as well as bearing engagement with opposite electrode surfaces 54a, 54d of the piezoelectric transducer 50. Another set of similar opposite metallic bearing rods 63, 64 maintain with their surfaces electric as well as mechanical bearing engagement with the exterior one-polarity rightward surface electrode portion 54b of upper ceramic strip 51 (as seen in FIG. 7) and with the opposite-polarity exterior surface electrode 54d of the other ceramic strip 52 of piezoelectric transducer 50. The opposite-polarity external terminal 45 is connected to the outer surface electrodes 54a, 54d of the two piezoelectric strips 51, 52 of the transducer 50 by means of bridging conductor 58. The two sets of metallic bearing rods- 61,62 and 63, 64 which maintain bearing contact engagement with the exterior electrode surfaces 54a, 54b and 54d also provide electrical circuit connections to these electrode surfaces as seen in FIG. 9. As shown by the and marks applied to the external circuit terminals 45, 46, they indicate the electrical polarization applied to these ceramic strips 51, 52 for securing the conjoined aiding vibratory transducer operation within the transducer 50 of FIG. 7 while connected in parallel aiding relation to'each other as shown by the circuit diagram of FIG. 9.

Like the piezoelectric transducer 40 of FIG. 6 when the piezoelectric transducer 50 of FIG. 7 is flexed or vibrated transversely to its planes or major surfaces, it generates a voltage across its circuit terminals 45 and 46 and vice versa.

Referring to FIGS. I, 2 and 6, the elongated piezoelectric transducer 40 is operatively mounted in its vibratory transducing position by mounting means comprising two sets or pairs of elongated bearing elements or rods 6l62 and 6364 extending transversely to the plane of FIG. 1. The bearing rods 6l64 are constructed and positioned both to maintain the transducer 40 (or transducer 50) in operative vibratory position in the transducer housing cavity 24. The two sets of metallic rolling bearing supports 61,62 and 63, 64 are longitudinally displaced along and are maintained in rolling bearing engagement with the so-displaced opposite electrode surface portions of the elongated mechanoelectric transducer 40. They also provide electric circuit connections to the engaged exterior opposite-polarity electrode surfaces 43a, 43d of the transducer of FIG. 6 and opposite bearing supports 63, 64 also provide circuit connection to opposite-polarity exterior electrode surfaces 54b and 54d of FIG. 7. The two bearing rods of each of the sets or assemblies of bearing rod 61, 62 and 63, 64 are positioned opposite eachother along and in contact engagement with the opposite electrode surfaces of longitudinally displaced sections of the transducer 40 (or transducer 50). To secure proper vibratory flexing of piezoelectric element 40, the bearing rods 6l64 have curved rolling contact surfaces which may be provided by giving them, for instance, a circular or cylindrical cross section to obtain rolling contact engagement with the exterior surfaces of transducer .beam 40 (or transducer beam 50 of FIG. 7) and thereby provide simple supports for the overhanging beam left of sections to the bearing rod set 61, 62 and to the right of bearing rod set 63, 64 (FIGS. 1, 6 and 7). The bearing rods 6l64 are mounted in the mounting means 33 which may be apertures within the opposite walls of the housing (FIGS. 3-4). The housing apertures 33 are dimensioned to securely hold the bearing rods 61- -64 to their operative positions and prevent their sliding out of operating contact engagement with the external surfaces of transducer 40.

The bearing rods 6l64 are shown formed of metal and provide the electrical connections to electrode surface coatings of the piezoelectric element 40. If the bearing rods 6l64 are of metal, their mountings in housing apertures 33 must insulate them as by insulating sleeves in a metallic housing or by making the housing 20 of an insulating plastic.

As shown in FIG. 2, the bearing rods 6l64 may have external terminal portions 65 exposed along the exterior of housing 20 to provide external electrical connections to the metallic terminal electrode coatings of piezoelectric transducer 40. Since the transducer device of the invention is of subminiature size, it is critically important to provide the miniature housing 20 with such substantial external electrical terminal connections formed by end portions 65 of these relatively large terminal metallic bearing rods.

Referring to FIGS. 1, 3, 4 and 5 on shelf 28 of each housing aperture 21, 22 and 23 rests or is positioned the peripheral region of each vibratable diaphragm 70. Each diaphragm 70 can be comprised of a thin strip of metal, e.g., a lightweight flexible aluminum, or of a thin strong plastic film, e.g. polyester films such as known MYLAR and similar films described in MODERN PLASTIC ENCYCLOPEDIA, I967, pages 549- 551 and 589. As an example, each diaphragm 70 may be formed of aluminum sheet 0.004-inch thick. Each diaphragm 70 has a minute aperture 72 which passes and has affixed thereto the outward end of its respective drive rod 80, as by a conventional wax junction or suitable cement. The central apertured portion of the diaphragm 70 can have additional body layers 73 of suitable material, such as 0.004 thickness aluminum, laminated and affixed thereto to provide the diaphragm with the mass and stiffness which gives it the desired vibratory operating characteristics within the required audiofrequency range.

Three spaced portions of the piezoelectric transducing element 40 are connected with drive rods 80 to the two laterally spaced diaphragms 70 or to all three diaphragms 70 to transmit vibratory movement therebetween. As seen in FIG. 2, the inward end of each drive rod 80 has curved embracing arms 81 and 82 which are biased to pivotally and drivingly engage the opposite side edges of longitudinally spaced connector sections of the piezoelectric element 40. The drive rods 80 may be formed of an electrically insulating material, for instance, of fiberglass reinforced epoxy plastic or of metal such as aluminumin which case the inward surfaces of rod arms 81, 82 should be coated with an insulating plastic layer.

Each drive rod 80 has a relatively narrow outer end portion 83 which passes through and is joined, as by wax or cement, to its diaphragm 70.

It is assumed that the subminiature acoustic transducer device of FIGS. 1 to 6 has only two laterally spaced vibratory acoustic diaphragms 70 (as seen at the upper side of FIGS. 1,

3 and 4). Each of such two laterally spaced diaphragms 70 is shown connected by its respective drive rods to the drive rod coupled end regions of elongated electromechanical signal transducer beams 40. As seen in FIGS. 1 and 6, in accordance with the invention, the so-diaphragm-coupled end regions of such transducer beam 40 are separatedfrom each other by at least one set bearing supported transducer beam sections which may be at the center of the transducer beam as shown in FIG. 6 by the set of opposite bearing rods 61-1, 62-2 shown by dash lines for mounting the transducer beam 40 in an efficient electromechanical signal transducing condition within its housing 20. Efficient electroacoustic transducer operation with such two laterally displaced curved bearing supports 61, 62 and 63, 64 having rolling engagement with their curved bearing surfaces along opposite exterior transducer surfaces at two longitudinally spaced sections of the elongated transducer 40 (or 50) disposed between and spaced from the diaphragm coupled end sections of such elongated transducer 40.

Reference is now made to an electroacoustic transducer device of the invention of the type just described having-in addition to the two laterally displaced acoustic diaphragms 70 overlying one side of the elongated transducer axesa third acoustic diaphragm 70 coupled by a third drive rod to the center region of the elongated transducer 40. In such threediaphragm coupled device, each two of the three longitudinally displaced diaphragm-rod coupled transducer sections is separated from the next longitudinally diaphragm-rod coupled transducer section by one of the two longitudinally displaced bearing sets 61, 62 and 63, 64 which engage with a rolling bearing support facing portions of the elongated mechanoelectric transducer 40. What was explained above with respect to the elongated mechanoelectric transducer 40 of such electroacoustic device of the invention applies also to such devices operating with analogous other types of elongated beam-shaped electromechanical transducers including that described in connection with FIGS. 7 and 9.

In the case of such just described three-diaphragm transducer device of the invention as shown in FIG. 1, the three drive rods 80 extend in opposite directions from the different successive connector sections of the transducer 40 to the two laterally displaced diaphragms 70 and the third opposite side central diaphragm to provide alternately directed diaphragmcoupling connections along the length of the piezoelectric or generally analogous longitudinal signal transducer 40. Furthermore, each of the bearing rod assemblies, e.g., 61-62 and 6364 is positioned between two alternately directed neighboring drive rods 80. The combination of the alternately directed drive rod connections with interposed alternately positioned bearing rod assemblies maximized the flexion amplitudes of the piezoelectric element 40 and its transduced signal output.

Each diaphragm 70 is protected by a cover or grille which is snapped into position thereover. The grilles 90 have peripheral flanged edges 91 which are biased inward to grip and be held in position by frictional engagement with adjacent housing portions. Alternatively, the grilles might be glued or otherwise secured in their positions. Each grille 90 has one or more apertures 92 to permit passage of sound and corresponding vibrations of the diaphragms 70 or vice versa.

If the transducer device shown is to operate with only two laterally displaced or with less than the maximum number of diaphragms 70, the undesired diaphragm can be removed and the corresponding apertures 21, 22, or 23 covered up with a similarly shaped thicker sound-impervious cover wall; or the corresponding drive rod 80 might be removed; or the opening 92 of overlying grille 90 plugged up.

The embodiments of this invention described above will suggest many variations and modifications to those skilled in the art, andis to be limited only by the appended claims.

Iclaim:

1. In a mechanoelectric acoustic transducer device comprisan elongated mechanoelectric vibratory transducer beam having an elongated axis for transducing vibratory motion into corresponding electric signals with vibrations transverse to said axis and vice versa,

a housing defining a cavity surrounding said beam and having at least two laterally spaced housing wall sections extending along one side of said beam axis,

said housing having at least two bearing members held in engagement with opposite exterior surfaces along an intermediate portion of said beam and supporting said beam in a vibratory transducing condition,

the improvement comprising:

a plurality of at least two distinct acoustic diaphragms vibratably carried along said laterally spaced wall sections over one side of said transducer axis and two drive rods, one for each diaphragm and connecting longitudinally spaced two connector sections of said beam to said diaphragm for transducing acoustic diaphragm signals into said electric transducer signals and vice versa,

said bearing members being positioned between said two beam connector sections;

a third acoustic diaphragm carried along a housing wall extending along the opposite side of said axis and a third drive rod connecting said third diaphragm to a third rodconnector section of said transducer disposed between said two transducer connector sections and means for causing said third diaphragm and its connection to said transducer to cooperate in aiding relation with said two diaphragms and said transducer.

2. In the mechanoelectric transducer device of claim 1,

the improvement also comprising:

said transducer having two axially extending opposite exterior longitudinal transducer surfaces two bearing rods constituting said bearing members with each bearing rod having a curved surface and carried by said housing in rolling bearing engagement with said opposite exterior transducer surfaces,

said housing having two sets of said bearing rods held along two longitudinally spaced sections of said transducer with each rod in said engagement with said opposite transducer surfaces,

said third drive rod having said third rod connective to a third transducer connector section disposed between said two sets of bearing rods.

3. In the mechanoelectric transducer device of claim 2,

the improvement also comprising:

each of said bearing rods having a curved exterior surface carried by said housing in rolling bearing engagement with the facing exterior transducer surface.

4. In the mechanoelectric transducer device of claim 2,

the improvement also comprising:

said transducer having two axially extending opposite exterior surfaces with each having a conductive electrode surface.

at least two of said oppositely positioned bearing rods having exterior conductive surfaces carried by said housing in bearing and electrical contact engagement with said opposite conductive transducer electrode surfaces and constituting circuit connections to said electrode sur faces.

5. In the mechanoelectric transducer device of claim 4,

the improvement also comprising:

each of said bearing rods having a curved exterior surface carried by said housing in rolling bearing engagement with the facing exterior transducer surface. 

2. In the mechanoelectric transducer device of claim 1, the improvement also comprising: said transducer having two axially extending opposite exterior longitudinal transducer surfaces two bearing rods constituting said bearing members with each bearing rod having a curved surface and carried by said housing in rolling bearing engagement with said opposite exterior transducer surfaces, said housing having two sets of said bearing rods held along two longitudinally spaced sections of said transducer with each rod in said engagement with said opposite transducer surfaces, said third drive rod having said third rod connective to a third transducer connector section disposed between said two sets of bearing rods.
 3. In the mechanoelectric transducer device of claim 2, the improvement also comprising: each of said bearing rods having a curved exterior surface carried by said housing in rolling bearing engagement with the facing exterior transducer surface.
 4. In the mechanoelectric transducer device of claim 2, the improvement also comprising: said transducer having two axially extending opposite exterior surfaces with each having a conductive electrode surface, at least two of said oppositely positioned bearing rods having exterior conductive surfaces carried by said housing in bearing and electrical contact engagement with said opposite conductive transducer electrode surfaces and constituting circuit connections to said electrode surfaces.
 5. In the mechanoelectric transducer device of claim 4, the improvement also comprising: each of said bearing rods having a curved exterior surface carried by said housing in rolling bearing engagement with the facing exterior transducer surface. 